IMPROVED STRUCTURAL THERMOPLASTIC COMPOSITES

Abstract: By (i) blending at least a thermoplastic matrix resin and one or more coupling agents, optionally with other adjuvants such as pigments, and (ii) providing the product of step (i) in a suitable size for use in the subsequent traditional aqueous dispersion process for making structural thermoplastic composites ("STC"), the resulting STC product has improved physical properties, particularly high temperature properties, with need for lower levels of additive materials, and improved surface appearance.

Description: Improved Structural Thermoplastic Composites Technical Field This invention relates to methods of preparing reinforced thermoplastic composites by wet-laid slurry processes so as to improve surface appearance and physical properties. Background of the Invention Structural thermoplastic composites ("STC") prepared from thermoplastic resins that are reinforced with various fillers, e.g. glass fiber, are well-known. In particular those prepared by the wet-laid slurry process developed originally in the paper-making industry have found increasing use for their suitably for thermoforming into structural and decorative components for such industries as those of the automotive and electrical appliances. Such STC is to be distinguished from the glass-mat thermoplastic composites ("GMT") prepared by dry processes which exhibit deficiencies in uniformity of properties when subjected to moulding conditions for complex applications. Poor flowability of the fiber in GMT subjected to heat-moulding for complex articles causes a lack of uniformity of properties and complex reinforcing designs. Uniformity of properties however is readily achieved in lighter moulded articles from the STC by the wet-laid process. However the STC articles to be produced are often visible to the end user and accordingly will preferably have excellent surface appearance in order to extend and enhance their utility previously exploited principally due to the excellent thermoforming capability, light-weight strength and toughness, and low cost. Additionally, advances in the automotive industry to meet energy conservation goals is requiring increasingly higher temperature tolerance of thermoplastic components and decreases in both the weight and cost of appropriate thermoplastic components. Means of preparing STC components by the wet-laid process appear in the patent literature. Documents in the field teach preparation of such STC sheet utilizing aqueous dispersions of various components, e.g. US-A-3 912 581, EP-A-0 039 292, FR-A-2 511 717, and EP-A-0 071 219. This early art addresses the aqueous dispersion of thermoplastic powder with reinforcing fiber and such other process aids and additives as desired. UK patents nos. GB-A-1 129 757 and GB-A- 1 329 409 address the use of a foamed, aqueous dispersion process for blending various fibers in the paper-making process, and EP-A-0 148 761 suggests that those processes could be used with thermoplastic powder in the preparation of STC sheet. Improvements in both processes for the manufacture and properties of STC, other than surface appearance, are addressed in US-A-4 481 075, US-A-4 645 565, EP-A-0 300 909, WO-A-91 10 702, WO-A-92 04 502, and WO-A-92 04 491. These documents all teach the use of processing aids and additives which increase the cost of the described STC. EP-A-0 281 475 (equivalent of US-A-4 913 774) discloses improved retention of adjuvants (additives) in aqueous dispersions for production of STC comprising intimately mixing the adjuvants with the thermoplastic resin, forming granules thereof and subsequently grinding the granules to form the powder to be used in the aqueous dispersion process. US-A-4 451 539 addresses the problem of surface properties for STC products and as a solution describes the preparation of surface foil having improved appearance produced by slurrying thermoplastic powder elements with a "dough" of ground polyolefin fiber elements and various additives, including pigments, coupling agents and ground reinforcing material of limited size, for subsequent dewatering in accordance with traditional papermaking technique. This foil is then transferred to the inside of two half molds for, e.g., thermoforming of reinforced polypropylene sheet, so as to form an improved appearance outer coating on the final part. However, such coated STC exhibits differential flow characteristics between the coating material and the reinforced polypropylene sheet and results in non-uniform appearance of the finished product. WO-A-92 04 399 describes improvements in the process for introducing colour into STC made by the wet-laid slurry process comprising surface-coating pigment particles onto thermoplastic material under powder form prior to providing into the aqueous slurry. This process is presented as an improvement over the process of EP-A-0 281 475 which is described as complicated, costly and not usable at an industrial level. Other than by the processes of US-A-4 451 539 and WO-A-92 04 399, the above art does not address solving the problem of the less than optimal surface appearance of the STC products described. Additionally the above documents do not address means of reducing additive material usage and weight of STC nor improving the high temperature properties. Accordingly it was sought to develop means improving the surface appearance of typical STC products without having to resort to the use of laminating and coating procedures previously known while reducing the necessary amounts of additives and improving high temperature properties. Invention Disclosure It has been surprisingly found that by i) blending at least a thermoplastic matrix resin and one or more coupling agents, optionally with other adjuvants such as pigments, and ii) providing the product of step i) in a suitable size for use in the subsequent traditional aqueous dispersion process for making STC, the resulting STC product has improved physical properties, particularly high temperature properties, with need for lower levels of additive materials, and improved surface appearance over previously known STC. In particular this invention comprises the use of a compounding process for preparation of thermoplastic composite particles comprising steps i) and ii) for the purpose of improving one or more of impact strength, tensile strength, flexural strength and surface appearance of structural thermoplastic composites prepared with said particles by wet-laid process. Best Mode and Examples of the Invention The blending of the thermoplastic matrix resin with coupling agent, and optional adjuvants, is accomplished by charging the components into a blending apparatus, heating to a temperature above the softening point of the resin while/or followed by intensive mixing. The resulting blend is then discharged or extruded, and allowed to cool. Particles are formed by extruding and cutting at sufficiently small size, or subsequently reducing in size the extrudate by physical means such as grinding into powder. The blending apparatus may be any internal mixing device useful for melt-blending and includes such as Banbury mixers, any of single-screw and multiple-screw extruders, and the like. The blending apparatus may be equipped with a heating jacket, or any other means of preheating the resin or physical mix of components, to assist reaching and surpassing the softening point temperature. Additionally or alternatively, blending conditions determined empirically for the selected blending apparatus and the mix of components can be set to generate sufficient heat for effective blending. Pulverization, or grinding into powder, is accomplished by use of standard plastics grinding equipment adjusted and operated so as to provide a powder size suitable for use in the wet-laid, or papermaking, process. Extrusion and cutting to appropriate size can be accomplished through use of conventional extrusion equipment fitted with small bore die, e.g. up to about 1.5 mm. Typically average particle diameter will be below about 1500 microns (micrometers), preferably not greater than about 1200 microns, most preferably about 1000 microns. If the particles are non-spherical the smallest dimensional limitation should be not greater than the average particle diameter described. Preferably the average particle diameter will be greater than 200 and more preferably more than 500. Above about 300 microns the dewatering phase of the wet-laid process will benefit from increased vacuum and/or use of an inclined screen to assure sufficiently fast drainage of the water and water-soluble components so that there is minimal differential settling and separation of the dispersed solids during the dewatering. The disclosure of WO-A-92 04 502 is particularly relevant to selection of particle size and means of dewatering in the wet-laid process. The wet-laid processes within which the invention is useful includes any of those processes employing aqueous dispersions to form STC known in the art. In particular, US-A-4 481 075, US-A-4 645 565, US-A-4 734 321 and US-A-4 929 308 are representative and are incorporated by reference for purposes of U.S. patent practice. Both of WO-A-91 10 702 and WO-A-92 04 502 provide state of the art description, and EP-A-0 071 219 provides additional background including the use of latex binders in aqueous dispersions. Broadly described the wet-laid process comprises the steps of: a) providing, or slurrying, the thermoplastic particles in an aqueous dispersion containing reinforcement material; b) dewatering the slurry of step a) on either of a two-dimensional screen or three-dimensional form to form a felt; and c) densifying the felt, generally by, i) drying said felt and ii) heat-pressing the felt, to form structural thermoplastic composite sheet or a three dimensional article. For the purposes of effective dispersion in the aqueous solution and retention of solid materials from that dispersion during dewatering, it is known to utilize various processing aids including dispersants, binders, flocculants, and various fibers or pulps of both celluosic and polymeric materials. Such materials and process aids may be used in this invention in their conventionally known manner and amounts. Selection of processing aids will preferably be done so as to reduce or minimize adverse reactions as described in the art. For example, WO-A-91 10 702 teaches the avoidance of process aids that react with either of silanized glass fiber or the reactive groups of the coupling agent. The STC of the invention include as thermoplastic resin any of those known in the art to be suitable for STC products, particularly the light and inexpensive polyolefin resins. Such resins include homopolymers and copolymers of C2-C10 alpha-olefins, polyamides, polyesters, polycarbonate, polystyrene, polyphenylene ether, polyphenylene sulfide, thermoplastic polyurethane, blends thereof, and the like. Additional listings and examples of suitable materials appear in the cited prior art, particularly US-A-4 481 075, EP-A-0 071 219 (based upon U.S. application no. 286,793 filed 27.07.81), and US-A-4 645 565. The disclosures of these documents are incorporated by reference for purposes of U.S. patent practice. Polypropylene is a preferred thermoplastic resin of significant current commercial use. As coupling agents, those that serve to compatibilize, or improve adhesion between, the reinforcing material and the thermoplastic resin will be suitable. For polypropylene homopolymer or copolymer based resins to be reinforced with glass fiber, the carboxyl-group containing polypropylene coupling agent Exxelor® PO 1015 of Exxon Chemical Company, U.S.A., used with silanized glass fiber, is particularly suitable in accordance with the invention. The disclosure of WO-A-91 10 702 (U.S. Application Serial Number 910,079 based on International application filed 09 January 1991) is particularly relevant and the related U.S. application is incorporated by reference for purposes of U.S. patent practice. Similarly for other thermoplastic resins, the coupling agent is typically a polar-group containing polymer that is both at least partially miscible, or reactive, with the resin and reactive with the glass fiber, that may itself be sized or coated to improve its reactivity in accordance with knowledge in the art. Such polar-group containing polymers are well known and often used additionally as compatibilizing components, see the following paragraph. US-A-3 862 265 exemplifies a method of preparation of polar-group containing polyolefins suitable for use with polyolefin resins or polymer blends containing them. The coupling agents are typically used an amount effective to improve the physical properties depending upon the adherence of matrix resin to reinforcing material, that amount is usually between greater than 0 and 25 wt. % based upon the total weight of resin, reinforcing material and coupling agent, more typically in the range of 0.1 - 10 wt. %. Compatibilizing components that serve to improve such properties as impact strength for blends, e.g., those containing polar thermoplastic resins, can be included. Suitable examples include the dispersed phase polymers of US-A-4 172 859 and US-A-4 174 358, and the polar-functionalized polyolefins of US-A-4 987 200 used as disclosed in EP-A-0 321 293 (for polyamides and polyesters). These disclosures are also incorporated by reference for purposes of U.S. patent practice. Additional examples for various thermoplastic polymer blends appear in "Reactive Polymers for Blend Compatibilization", N.C. Liu and W.E. Baker, Advances in Polymer Technology, Vol. 11, No. 4, 249-262 (J. Wiley & Sons, Inc., 1992). Typically such compatibilizer compositions are used in amounts ranging from 5 - 30 wt. % based upon the weight of the resin plus compatibilizer, more typically from 10 - 25 wt. %. Reinforcing materials generally suitable in accordance with the invention include those known in the STC art. Reinforcing fiber includes those of glass, carbon, aramid, thermoplastic (polyamide, polyester, etc.), metals (stainless steel, aluminum, nickel, etc.), ceramic (refractory ceramic fibers, boron, silicon carbide, etc.), vegetable matter (wood, paper, jute, sisal, bamboo, etc.) and mixtures (i.e., hybrid composites). The glass fiber may be any of E-glass (general purpose), S-glass and R-glass (high mechanical performance), D-glass (high dielectric performance), aluminum or graphite coated (EMI shielding), the E- and S-glass are preferred for the light weight, low cost polyolefin resin based STC products. Any of these may be pre-treated with various coatings to improve their adhesion to the thermoplastic through the use of the coupling agent. For example, organosilane sizing of glass fiber for use with polypropylene resin and acid-modified polypropylene coupling agents is particularly effective. The reinforcing fibers will comprise from 10 to 60 wt. % of the total STC product compositions, typically 20 to 50 wt. %. Fiber length is typically from above about 4.5 up to about 50 mm, preferably above 6 up to 30 mm. Fiber diameter typically ranges from 7 to 25 microns (micrometers), preferably 10 to 18 microns. Reinforcing fiber is preferably added directly into the aqueous dispersion of the wet-laid process to avoid or minimize fiber breakage in the compounding and improve effective dispersion. Fillers may also contribute as reinforcing material (or as EMI shielding, conductivity enhancer, flame retardant, etc.), although more typically they are used where capable of reducing the use of more expensive or heavier components without significantly reducing desired properties in the end product. Within the purview of the present invention, there are two filler parameters which strongly influence the mechanical properties of a filled long glass fibre reinforced plastic. These parameters are: the particle size of the filler and the purity of the filler. Reduced particle size was found to result in increased tensile strength. The presence of impurities, and in particular those with hard or sharp particles, was found to be detrimental to impact performance. Useful fillers include aluminum flakes, alumina trihydrate, magnesium hydroxide, calcium carbonate, kaolin, barium sulfate, zirconium, silica, glass flake or spheres (solid or hollow), polymeric flake or spheres (solid or hollow), polytetrafluoroethylene, mica, talc, silicon carbide, wood flour, nutshell flour and the like. Provision of the fillers can be by melt-blending with the resin/coupling agent or by direct introduction into the aqueous dispersion. Polymeric fillers from recycled plastic sources are also useful in accordance with this invention. Examples include recycled neat resin at least partially compatible, or rendered so by use of compatibilizers, with the matrix resin, or recycled GMT or STC. US-A-5 030 662 addresses extrudable recycled polymer blends which if provided in the suitable size range for the wet-laid process can be effectively utilized as filler. It can be provided in the initial blending step or by direct addition into the aqueous dispersion. Similarly the polymer and recycled polymer blends of pending priority application GB 9219961.1 (unpublished, filed 22 September 1992) can be effectively used. Though such polymeric fillers may be of similar softening point as the thermoplastic resin and thus useful as a component thereof, they are also included herein. Where the recycled plastic contains reinforcing fibers within the range desirable for STC it may be utilized without prior compounding, so long as it is of the correct particle size. If the fiber size is too great, compounding in the blending step contributes to the reduction of size of the fiber introduced with the polymeric filler. Typically fillers will comprise up to about 25 wt. % based on total product weight, more typically in the range from above 0 to about 10 wt. %. Colorants are also often used, typically in the form of pigment or dye. Carbon black, titanium dioxide and other organic and inorganic pigments and dyes known in the plastics industry will be useful in accordance with this invention. Masterbatch compounds of the pigment or dye with other components or with compounding polymers or waxes are particularly useful for retaining the pigments and dyes in the accumulated powder and fiber web or mat created upon dewatering, if not compounded prior to introduction into the aqueous dispersion. The disclosure of WO-A-92 04 399 is particularly relevant. It is preferred that solid colorants, e.g., carbon black, or masterbatched compounds including dyes or pigments, be blended initially with the thermoplastic resin and coupling agent to form an intimate blend for subsequent provision in suitable particle size. However, acceptable STC product can also be obtained by dry mixing the blended resin/coupling agent particles with the colorant, or providing the colorant directly into the aqueous dispersion prior to dewatering as, for example, in WO-A-92 04 399. It is important to note that the particle size of the colorant can affect the final properties of sheet prepared form the compositions, and those of the final product made from the sheet. It is generally known that the smaller the particle size of carbon black the higher is the degree of blackness (also known as jetness) and the tinting strength. The colouristic properties of a carbon black are strongly influenced by the primary particle size, with the smallest particles giving the highest jetness (i.e., intensity of blackening) and the greatest tint strength. In order to achieve a good appearance, it is necessary to use a medium or high colour carbon black (i.e., < 20 nm particle size) when pigmenting STC. It has been now discovered that the smaller the particle size of the carbon black the lower is the tensile strength of the sheet. It has been found that utilization of colorant in average particle diameter not smaller than about 15 nm and not larger than about 20 nm in a sheet renders optimum performance and appearance. Smaller particles of less than 15 nm generally minimized tensile strength to a sheet while particles of larger than 20 μm imparts a less than suitable appearance to a sheet. Additional modifying additives affecting the end properties of the STC product may be optionally included in the initial melt-blending of the resin and coupling agent, in dry mixing of the blended resin/coupling agent particles with other dry ingredients, or in the aqueous dispersion of the wet-laid process at any time prior to dewatering. Such additives may include heat, light and UV stabilizers, antioxidants, antiwear agents, nucleating agents, flame retardants, smoke suppressants, conductivity improver additives, antistatic, slip additives and the like. Typically such additives are used in amounts of above 0 - 10 wt. % based upon total product weight, more typically up to 5 wt. %. Though not intended as a limitation on the invention as described, it is believed that the intimate blending of the components allows the preparation of particles having an improved homogenous blend of ingredients that is retained through subsequent processing. When the final thermoforming is accomplished the resulting STC thus exhibits the improved appearance and physical properties, with reduced amounts of the necessary components, that are believed to result from the increased homogeneity of the thermoplastic resin, coupling agent and other included components, such as pigment. Typical industrial applications include any of those where either of three- dimensional or two-dimensional thermoformable STC products are used. Typically the dewatered felt or web is deposited on a flat screen, dried, heated and pressed into sheet in accordance with knowledge in the art, see the background art addressed in this application. During heating and pressing the thermoplastic resin/coupling agent powder in the web melts and flows about the reinforcing fiber, carrying with it or incorporating the other colorants, additives, etc. The resulting product is flat STC sheet which is thermoformable into many possible shapes. Alternatively, the slurry containing the powder, reinforcing material, etc. is deposited and dewatered directly upon a three-dimensional form for subsequent thermotreating to form the final product. The reinforced STC products formed from sheet or upon a form are useful as automotive or other transportation industry parts, communication/electronic equipment housings, construction goods, sporting goods, domestic appliances, furniture, luggage, various containers for storage and shipping, and the like. The following examples are presented to illustrate the foregoing discussion. All parts, proportions and percentages are by weight unless otherwise indicated. Although the examples may be directed to certain embodiments of the present invention, they are not to be viewed as limiting the invention in any specific respect. Example I A series of comparative tests of finished product properties were conducted on compositions described below in accordance with standard testing procedures and yielded the results tabulated in Table I (room temperature) and Table II (elevated temperature). Additionally visual inspection was conducted of the prepared samples and rated as poor ("P"), fair ("F"), and good ("G") and very good ("VG" ). Each sample was prepared by the wet-laid process according to WO-A-92 04 502. The described components were slurried in an aqueous dispersion comprising 5 g 1 solids in the aqueous dispersion, with 10 wt. % based upon the weight of glass fiber of Cartaspers DS1 Liquide® of Sandoz S.A., Switzerland as a dispersing aid, and 2 wt. % based upon total dispersion weight of SWP Y600®, Mitsui & Co. France S.A., France, as polyolefin pulp. This dispersion was subsequently dewatered upon an inclined screen, dried (163°C), heated (250°C.) and pressed into a predensified blank. Each blank was subsequently molded into suitable plaques for testing. Samples A and B consisted of charging a 1.1 1. type BR Banbury internal mixer with the components as described below. Intensive mixing was conducted for 3 minutes after a temperature of 155 °C. was reached. Sample B was provided jacket heating additional to the heat of mixing, sample A was not. The thus blended mixtures were allowed to cool to a room temperature and then ground. Grinding was accomplished by first breaking the solidified mixture into small lumps which were then fed to a type GK 205-K grinder from Rapid Maskin AB., Sweden. This converted the mixture to a powder having a maximum particle size of approximately 1 mm (1000 microns). This powder was then slurried with silanized glass fiber reinforcement (type 778-0 of Owens-Corning, Inc., U.S.A., diameter 16 micron, length 13 mm) in an amount targeted for 40 + 2 wt. % glass, based upon the total weight of dry components, as described above. Sample C was prepared by slurrying together the glass fiber and components below but without previously melt-blending those components. The resin was provided as reactor granules having a particle size of not greater than about 1500 micron. The coupling agent was separately pulverized such that particle size was below 600 micron. The resin particles, coupling agent powder, pigment masterbatch and antioxidant were dry blended prior to introduction into the aqueous dispersion. Sample D was prepared as for samples A and B but the pigment was omitted from the melt-blending step and dry coated onto the ground polymer particles in accordance with WO-A-92 04 399. Sample E was similarly prepared but the coupling agent was omitted instead of the pigment and introduced directly into the aqueous dispersion (as with sample C), the pigment was included in the melt-blending step. Example I: Composition A B C D E F polypropylene, PD 3505G (Exxon Chemical Co., U.S.A.) 86.4 87.2 85.7 86.4 86.4 95 maleated polypropylene, EXXELOR® PO 1015 (Exxon Chemical Co., U.S.A.) 10.4 9.8 10.4 10.4 10.4 3.0 Irganox® B-232 (Ciba-Geigy S.A., Belgium) 2.2 2.1 2.2 2.2 2.2 0.4 2 Holcobatch® C Black 939098F (Holland Colours B. V., Netherlands) 1 0.9 1.7 1 1 0 Plasblak® UM 2014 (Cabot Plastics Belgium S. A., Belgium) 0 0 0 0 0 1 Ash content 1 (wt. %, total comp.) 37.4 38.0 38.1 36.8 37.6 38.3 note * : inorganic residue upon burning final composition in air at 750°C. for 30 min. (includes glass fiber and inorganic fillers/additives) note 2 : Also includes 0.6 wt. % Irganox® PS 802 (Ciba-Geigy S. A., Belgium) TABLE I (23°C.) A B C l E F flexural modulus (secant ) (MPa) DIN 53452 5733 5649 5482 5610 5758 5730 flexural modulus (tangent) (MPa) DIN 53452 5686 5545 5593 5305 5608 5568 flexural strength (MPa) DIN 53452 170 179 169 169 164 175 tensile strength (MPa) DIN 53455 113 129 114 110 112 114 impact strength (unnotched Charpy) (kJ/m 2 ) ISO 179 67 72 72 60 57 67 Appearance VG VG F G G VG TABLE π (120°C.) A B C D £ F flexural modulus (secant) (MPa) DIN 53452 3284 3530 3647 3509 3287 3746 flexural modulus (tangent) (MPa) 2993 3236 3384 3139 3150 3071 DIN 53452 flexural strength (MPa) DIN 53452 74 76 71 74 65 84 tensile strength (MPa) DIN 53452 86 87 81 78 80 91 impact strength (kJ/m2) (unnotched Charpy) ISO 179 59 66 63 56 56 66 Appearance VG VG F G G VG Both tables generally show improvement in tensile strength, flexural strength and surface appearance for samples A and B of the invention over C, D and E. Impact strength is improved at high temperature when jacket heating during blending was provided. The Table II values demonstrate the significantly improved high temperature properties, and specifically the improved retention of tensile strength from room to elevated temperature from utilizing the blending step of the invention. Sample F illustrates improved properties obtained by compounding in accordance with the invention, even with significantly decreased amounts of coupling agent and stabilization package. Example II In this series of test compositions, compounded particles in accordance with the invention were mixed in the aqueous dispersion with particles prepared in accordance with the description in WO-A-92 04 399. Sheet prepared from the mixed aqueous dispersions were then compared under standard testing conditions as done in Example I. For this example the glass fiber was silanized fiber reinforcement type M-189 of Schuller International Inc., U.S.A. having 16 micron (micrometer) diameter and length of 13 mm. Fiber loading was targeted at 42 + 2 wt. % based upon the total weight of dry components. Sample A was prepared as done for Samples A and B of Example I, with the polypropylene resin and other adjuvants compounded by blending prior to being dispersed in the aqueous dispersion. This blending step was conducted with the addition of jacket heating of the blending apparatus. Examples B-E were prepared by coating of the adjuvants onto granules of the polypropylene resin (as in WO-A- 92 04 399) and mixed with varying proportions of Sample A particles in an aqueous dispersion. Pre-densified blanks and plaques were prepared as for Example I. The test results are reported in Tables III and IV. Example II: Composition A B* C* ι>ι τ polypropylene, PD 3505G (Exxon Chemical Co., U.S.A.) 96.2 23.9 47.6 71.3 95.1 maleated polypropylene, EXXELOR® PO 1015 (Exxon Chemical Co., U.S.A.) 1 0.2 0.5 0.7 0.9 Irganox® B-232 (Ciba-Geigy S.A, Belgium) 0.4 0.6 1.1 1.7 2.2 Irganox® PS802 (Ciba-Geigy S.A., Belgium) 0.4 0 Holcobatch® C Black 939098F (Holland Colours B.V., Netherlands) 2 0.4 0.9 1.3 1.8 Sample A content (wt. %) 100 74.9 49.9 25 0 note 1 : Listed components do not include those introduced with Sample A TABLE in (23°C.) TABLE IV (120°C.) Both tables generally show improvement in flexural modulus and appearance as the compounded composition A is increased in amount relative to the total blend. Both of flexural strength and tensile strength are also significantly improved at elevated temperature while retaining the advantages of appearance and flexural modulus. Example III To provide an objective measure of surface improvement two sample blanks prepared as in Example I, of Ex. II A of the invention and Ex. II E (comparison), were subjected to surface roughness testing. Each was measured for surface roughness index (RA) defined as being the first moment of amplitude of surface distortion as measured by a SURFCOM HOB, from Tokyo Seimitsu Co. Ltd., Tokyo, Japan. The A sample exhibited a measured R^ of 0.5-0.9 micron (micrometer) and the E sample exhibited an R^ of 5.0-5.6 microns (micrometers). Visual observation of each sample revealed that the A sample had a more uniform black color while the E sample had clearly observable glass fiber at the surface creating a whitish appearance. Example IV. V. and VI The following examples illustrated in Table V show the mechanical properties of typical STC materials prepared with a matrix comprising 77.6% PD 3505G polypropylene (Exxon), 9.4% Exxelor PO 1015 (Exxon), 2% Irganox B-232 (Ciba-Geigy), 0.9% Holcobatch C Black 939098F (Holland Colours), and 10.1% of one of Christalia C-16, Christalia OC-16 or Christalia OC-30 barium sulphate (Garrot-Chaillac). Comparing Christalia OC-16 (3.5 μm) with Christalia OC-30 (6 μm) the superior tensile strength of the material made with the smaller particle size filler is evident. Comparing Christalia C-16 of > 98% purity with Christalia C-16 of ≥ 96% purity demonstrates the advantage in impact properties obtained in using barium sulphate having lower levels of impurities. The barium sulphates used in these examples were the natural mineral and not chemically derived. TABLE V EXAMPLE IV EXAMPLE V EXAMPLE VI Christalia C-16 Christalia OC-16 Christalia OC-30 Size: 3.5 μm (ave) Size: 3.5 μm (ave) Size: 6 μm (ave) Purity: > 98% Purity: > 96% Purity: > 96% flexural modulus (secant) (MPa) 5505 5388 5199 DIN 53452 flexural modulus (tangent) 5392 5259 5103 (MPa) DIN 53452 flexural modulus Strength (MPa) 169 161 159 DIN 53452 tensile strength (MPa) 117 118 112 DIN 53455 impact strength (unnotched Chaφy) (kJ/m2) 65 61 59 ISO 179 Ash (%) 42.14 41.08 41.2 Examples VII. VIII. and IX The following examples illustrated in Table VI demonstrate the mechanical properties of typical STC materials comprising 29± 2% fibre glass (Type 778- Owens Corning), 2% SWP Y600 (Mitsui), 61± 1% PD 3505G polypropylene (Exxon), 6% Exxelor PO 1015 (Exxon), 0.6 0.15% Crodamide OR (Croda Universal), and a stabilization package of either 1.5% Irganox B-225 (Ciba-Geigy), 1% Irganox B 215 (Ciba-Geigy) or 1% Irganox B-215 + 0.5% Rhodianox TBM6 T (Rhδne-Poulenc). The carbon black pigments used to pigment these materials were Elftex 435 (Cabot), Black Pearls 800 (Cabot), Black Pearls 900 (Cabot) and Color Black FW (Degussa). The carbon black contents were between 0.1 and 0.5%. The carbon black content was not found to have a significant effect within the range studied. The properties listed in Table VI, below, are an average of several trials made with each carbon black composition with both antioxidant packages. TABLE VI Carbon Black Particle Size (nm) Tensile Strength (MPa) average minimum maximum Color Black FW 1 (Degussa) 13 67 63 74 Black Pearls 900 (Cabot) 15 75 73 78 Black Pearls 800 (Cabot) 17 81 74 87 Elftex 435 (Cabot) 27 83.5 80 87 As can be observed, the sheet with a particle size of less than 15 has insufficient tensile strength. The sheet with a particle size of 27 nm had an unacceptable coloration due to the larger particle size of the carbon black. Although the invention has been described with respect to particular materials, means and embodiments it is to be understood that the invention is not limited to the particulars disclosed and extends to all equivalents within the scope of the appended claims. The following is claimed:

Claims: Claims 1. An improved process for the preparation of a structural thermoplastic composite object comprising the steps of i) providing thermoplastic matrix resin particles and reinforcing material into an aqueous dispersion, ii) dewatering upon a screen or form the dispersion of step i) to prepare a felt, and iii) densifying said felt to form said object, the process characterized in that said thermoplastic matrix resin particles comprise a blend of at least one thermoplastic matrix resin and one or more coupling agents, optionally with other adjuvants such as pigments. 2. The process according to claim 1 wherein said object is a sheet and said dewatering step is done upon a two-dimensional screen. 3. The process according to claim 1 wherein said object is a three-dimensional article and said dewatering step is done upon a three-dimensional form. 4. The process according to any of claims 1 - 3 wherein said thermoplastic matrix resin particles additionally comprise at least one of colorant, filler or modifying additive. 5. The process according to any of claims 1 - 4 wherein said thermoplastic matrix resin is polypropylene and said coupling agent is acid-modified polypropylene. 6. The process according to any of claims 4 - 5 wherein said filler is barium sulphate. 7. The process according to any of claims 1 - 6 wherein said colorant comprises carbon black. 8. The process according to claim 7 wherein the carbon black is in particles in the size of 15-20 nm. 9. The process according to any of claims 1-8 wherein said reinforcing material is silanized glass fiber. 10. The product made according to the process according to any of claims 1-9 having improved characteristics of one or more of impact strength, tensile strength, flexural strength and surface appearance.

Inventors: DEVOREST YANN, JACOBS PAUL M, DEVOREST, YANN, JACOBS, PAUL, M.
Applicants: DEVOREST YANN, EXXON CHEMICAL PATENTS INC, JACOBS PAUL M, DEVOREST, YANN, EXXON CHEMICAL PATENTS INC., JACOBS, PAUL, M.
Application year: 1994
Main classification: D21H21
IPC codes: C08J3, D21H13, D21H17, D21H21